1. Field of the Invention
This invention relates to semiconductor processing. More particularly, this invention relates to a method of sequential deposition of high-K Al2O3 films on a substrate.
2. Description of the Related Art
The semiconductor industry continues to strive for larger production yields while increasing the uniformity of layers deposited on substrates having increasingly larger surface areas. These same factors in combination with new materials also provide higher integration of circuits per unit area of the substrate. High-K dielectrics are an example of new materials currently investigated. These materials are being investigated as a potential replacement for SiO2 as both gate and DRAM dielectrics. The present and future requirements for SiO2 in MOS structures relate to thicknesses less than 5 nm. The equivalent thicknesses may be achieved with higher K materials physically thicker than the SiO2 layers. The choice of suitable high-K dielectrics is typically directed to materials with relatively large band gaps and high dielectric constants. The band gap of Al2O3 is 9 eV, which is considerably larger than that of most high-K materials and comparable to that of SiO2. Also, the dielectric constant of Al2O3 is 9, which is more than two times greater than that of SiO2. Therefore, Al2O3 is a suitable high-K replacement for SiO2.
As circuit integration increases, the need for greater uniformity and process control regarding layer thickness rises. As a result, various technologies have been developed to deposit layers on substrates in a cost-effective manner, while maintaining control over the characteristics of the layer. Chemical Vapor Deposition (CVD) is a common deposition process employed for depositing layers on a substrate. CVD is a flux-dependent deposition technique that requires precise control of the substrate temperature and precursors introduced into the processing chamber in order to produce a desired layer of uniform thickness. These requirements become more critical as substrate size increases, creating a need for more complexity in chamber design and fluid flow technique to maintain adequate uniformity.
Another deposition process that demonstrates superior step coverage is a sequential deposition technique known as Atomic Layer Deposition (ALD). ALD has steps of chemisorption that deposit monolayers of reactive precursor molecules on a substrate surface. A drawback with ALD of Al2O3 films is that the deposition rate is much lower than conventional CVD methodologies, in part, because many of the precursors employed are highly viscous or solid. This increases the time required to introduce the precursors into a processing chamber and, thus, processing time.
Thus, a need exists, to provide an improved technique to form Al2O3 films employing sequential deposition techniques, such as Atomic Layer Deposition.
Disclosed is a method and apparatus for depositing high-K Al2O3 films on a substrate disposed in a processing chamber employing liquid precursors having low viscosity. In this manner, the time required to form an Al2O3 film using ALD techniques is reduced. The method features sequential flow of aluminum and oxygen precursors into the processing chamber. To that end, the aluminum precursor is chemisorbed onto the wafer surface when it flows into the processing chamber. The non-chemisorbed aluminum precursor is then purged from the processing chamber, followed by introduction of the oxygen precursor. The oxygen precursor reacts with the chemisorbed layer, creating a monolayer of Al2O3. Finally, excess oxygen precursor and by-products of the reaction are purged from the processing chamber completing an ALD cycle. To obtain the desired film thickness, multiple ALD cycles are repeated. The apparatus includes features that carryout the steps of the method.